Methods for fabricating shapes by use of organometallic ceramic precursor binders

Abstract

This invention relates to the discovery of organometallic ceramic precursor binders used to fabricate shaped bodies by different techniques. Exemplary shape making techniques which utilize hardenable, liquid, organometallic, ceramic precursor binders include the fabrication of negatives of parts to be made (e.g., sand molds and sand cores for metalcasting, etc.), as well as utilizing ceramic precursor binders to make shapes directly (e.g., brake shoes, brake pads, clutch parts, grinding wheels, polymer concrete, refractory patches and liners, etc.). In a preferred embodiment, this invention relates to thermosettable, liquid ceramic precursors which provide suitable-strength sand molds sand cores at very low binder levels and which, upon exposure to molten metalcasting exhibit low emissions toxicity as a result of their high char yields of ceramic upon exposure to heat.

We claim: 
     
       1. A process for fabricating shaped articles by casting comprising: at least partially coating the surface of at least one sand with at least one hardenable, solventless liquid, organometallic, ceramic precursor binder comprising a material selected from the group consisting of polysilazane, polyureasilazane, polythioureasilazane and polysiloxane to form a sand/binder mixture;   forming at least one shape from said sand/binder mixture;   hardening said sand/binder mixture by a crosslinking mechanism to form at least one sand mold, shell, or core; and   casting at least one metal or metal matrix composite into the resulting hardened at least one sand mold, shell, or core to form at least one shaped metal or metal matrix composite article.   
     
     
       2. A sand/binder mixture comprising (1) at least one sand and (2) at least one at least one hardenable, solventless liquid, organometallic, ceramic precursor binder, said binder comprising at least one metal-carbon bond, at least partially coated on the surface of said at least one sand characterized in that said sand/binder mixture is hardenable by a crosslinking mechanism. 
     
     
       3. The sand/binder mixture of claim 2, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder comprises at least one composition selected from the group consisting of polysilazane, polyureasilazane, polythioureasilazane, and polysiloxane. 
     
     
       4. A process for fabricating shaped articles by casting, said process comprising (1) at least partially coating the surface of at least one sand with at least one hardenable, solventless liquid, organometallic ceramic precursor binder, said binder comprising at least one metal-carbon bond, to form a sand/binder mixture, (2) forming at least one shape from said sand/binder mixture, characterized by hardening said sand/binder mixture by a crosslinking mechanism to form at least one sand mold, shell, or core, and (3) casting at least one metal or metal matrix composite into the resulting hardened at least one sand mold, shell, or core to form at least one shaped metal or metal matrix composite article. 
     
     
       5. The process of claim 4, wherein said at least one sand comprises at least one of silica sand, zircon sand, olivine sand, magnesite sand, chromite sand, hevi-sand, chromite-spinel sand, carbon sand, unbonded sand, washed sand, crude sand, lake sand, bank sand, naturally bonded sand, silicon carbide sand, chamotte sand, mullite sand, kyanite sand, sillimonate sand, aluminum sand, corundum sand, and combinations and mixtures thereof. 
     
     
       6. The process of claim 4, wherein said at least one hardenable, solventless liquid, organometallic ceramic precursor binder comprises at least one composition selected from the group consisting of polysilazane, polyureasilazane, polythioureasilazane, and polysiloxane. 
     
     
       7. The process of claim 4, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder comprises alkenyl, alkynyl, epoxy, acrylate or methacrylate groups. 
     
     
       8. The process of claim 4, wherein said at least one hardenable, liquid, organometallic, ceramic precursor comprises polysilazane. 
     
     
       9. The process of claim 4, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder comprises at least one polyureasilazane. 
     
     
       10. The process of claim 4, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder comprises at least one polysiloxane. 
     
     
       11. The process of claim 4, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder comprises titanium, zirconium, aluminum, or silicon. 
     
     
       12. The process of claim 11, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder comprises silicon. 
     
     
       13. The process of claim 4, wherein said at least one hardenable, liquid, organometallic, ceramic precursor comprises oxygen or nitrogen. 
     
     
       14. The process of claim 4, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder comprises nitrogen. 
     
     
       15. The process of claim 4, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder comprises alkenyl groups. 
     
     
       16. The process of claim 15 wherein said alkenyl groups comprise vinyl groups. 
     
     
       17. The process of claim 4, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder comprises from about 0.1% to about 20% of said sand/binder mixture based on the total weight of said sand/binder mixture. 
     
     
       18. The process of claim 17, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder comprises from about 0.1 wt % to about 5 wt % of said sand/binder mixture based on the total weight of said sand/binder mixture. 
     
     
       19. The process of claim 18, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder comprises from about 0.1 wt % to about 2 wt % of said sand/binder mixture based on the total weight of said sand/binder mixture. 
     
     
       20. The process of claim 4, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder is hardened through the application of at least one of heat, UV irradiation, or laser energy. 
     
     
       21. The process of claim 20, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder is hardened through the application of heat. 
     
     
       22. The process of claim 21, wherein said at least one hardenable, liquid, organometallic, ceramic precursor binder further comprises at least one free radical generator. 
     
     
       23. The process of claim 22, wherein said at least one free radical generator comprises at least one peroxide or at least one azo compound. 
     
     
       24. The process of claim 23, wherein said at least one peroxide comprises dicumyl peroxide.